The nature of immunological memory in T cell-mediated antibacterial immunity will be studied further. Experiments will be performed to investigate whether the level and duration of immunological memory of the T cell-mediated type is determined by the level and duration of primary infection, and hence by the level and duration of the primary active response. More fundamentally, the experiments will determine whether the short-lived, replicating T cells generated to mediate active immunity are the antecedents of the longer-lived, non-replicating T cells that carry memory and which thus enable the host to regenerate replicating mediator T cells at a faster rate in response to secondary infection. This will involve determining whether the adoptive transfer of immunological memory can be achieved by an infusion of lymphocytes harvested at the peak of the active primary response, and if so, whether the transfer is either suppressed or ablated by treating the cells with agents that selectively destroy replicating cells. Again, since replicating mediator T cells emigrate in large numbers into peritoneal exudates at the exclusion of long-lived lymphocytes, peritoneal exudate cells will also be examined for their capacity to transfer a state of long-lived memory. They will be employed both before and after being subjected to a velocity sedimentation gradient in order to separate the larger replicating blast T cells from smaller non-replicating T cells. These as well as other procedures will be employed to further investigate whether the T cells which carry memory are the same T cells that initiate delayed sensitivity reactions. BIBLIOGRAPHIC REFERENCES: North, R.J. Nature of memory in T cell -mediated antibacterial immunity: Anamnestic production of mediator T cells. Infect. Immun. 12, 754 (1975). North, R.J. and Deissler, J.F. Nature of memory in T cell-mediated antibacterial immunity: Cellular parameters that distinguish between the active immune response and a state of memory. Infec. Imm. 12, 761 (1975).